The long term objective of our research is to understand how the eukaryotic cell designates certain regions of DNA as replication origins, regulates their firing in a tissue- and temporal-specific manner, and coordinates this activity with the transcription of nearby genes. The model system being utilized is the developmentally regulated amplification of the chorion gene clusters in Drosophila ovarian follicle cells, which exhibits each of these levels of regulation. The control of DNA replication, and the phenomenon of gene amplification, are particularly relevant to the study of human cancers. Several proto- oncogenes and tumor-suppressor genes are implicated in the regulation of DNA replication. Moreover, several tumors are associated with the specific amplification of proto-oncogenes; and specific gene amplification is implicated in the development of resistance to chemotherapeutic agents. To begin to understand chorion gene amplification the trans-acting factors are being cloned and analyzed. CF2 is a gene encoding a protein which binds specifically to cis-acting amplification regulatory sequences, which was cloned by expression screening. The phenotype of CF2 mutations will be assayed, and the biochemical function of CF2 in amplification will be determined by introducing altered CF2 genes into transgenic flies. K43 is a gene identified by mutations, which is required in trans for amplification. K43 will be cloned and sequenced, and its biochemical role in amplification will also be determined.